Known has been an infrared absorption gas analyzer (patent RU 2292039, IPC G01N21/61, publ. 2005-02-18), hereinafter referred to as a gas analyzer, that comprises a control unit, an optical gas cell, an infrared radiation (hereinafter referred to as IR) source and an IR detector. The IR radiation source is installed at the cell inlet, while the IR radiation detector is installed at the cell outlet. The control unit is adapted to process the IR radiation, received by the detector, to display the results of the processing. Also, the IR radiation source has a spherical mirror reflector. The optical gas cell includes operational and reference chambers, wherein the operational chamber is shaped like a hollow frustum of a cone with an internal spherical mirror reflector and is installed immediately within the reference chamber in the optical axis with the IR radiation source, whereas the IR radiation detector comprises a focusing unit and is installed along an optical axis perpendicular to the first one. A mirror splitter and a rotating disc with a profile window are placed at the cross point of these axes.
This gas analyzer has such significant disadvantages as:                high energy consumption due to the loss of a substantial energy portion of the IR radiation source at the mirror reflector and due to the IR radiation flow interruption by the disc with a profile window, because only small areas within the wide spectrum of the IR radiation of the source are used;        reduced operational reliability due to having a multitude of mechanical parts, such as, for example, the rotating disc with the profile window and a rotating optical filter; and        increased overall dimensions resulting mainly from a large number of space consuming mechanical parts, and spherical mirror reflectors, with their mutual allocation.        
A gas analyzer is known (EPA 2169384, IPC G01N21/35, publ. 2010-03-31) intended for the creation of a multi-component apparatus, to be used within stationary facilities or at mobile medical stations for monitoring human breath gases with sufficient accuracy provided by means of compensating the external influences upon the radiation path trajectory. Herein, this task is solved through the use of an infrared radiation source, a gas cell, a dichroic beam splitter, an analyzing filter, a reference detector, and a measuring detector. In this case, the dichroic beam splitter is adapted to change the beam angle depending on the gas analyzed. The dichroic beam splitter is installed at 45° to the normals of the photodetectors located at 90° to each other.
The disadvantages of this analyzer include large dimensions and high energy consumption.
Known from Russian patent 2372606, IPC G01N21/03, publ. 2009-11-10, is a miniature multi-path mirrored optical cell. The cell fails to protect against temperature external conditions.
Known has been an infrared gas analyzer (U.S. Pat. No. 6,114,700, IPC G01N21/05, publ. Sep. 5, 2000), wherein photovoltaic detectors are used as infrared radiation detectors. However, the use of the photovoltaic detector in the known gas analyzer does not provide a balance of high detectability and fast response.
Also known has been an optical gas sensor device based on the immersion diode optical pairs is known (RU 75885, IPC G01N21/35, publ. Aug. 27, 2008), comprising a gas cell, the reflecting surfaces of which form an optical scheme for generating a probe radiation beam, as well as a probe IR radiation source including a light-emitting diode (LED) and a photodetector including a photodiode, which are mechanically connected to the gas cell body. The gas cell comprises mechanical adjusting elements, the light-emitting diode and photodiode being implemented with the use of immersion optics (immersion diodes) and rigidly connected to the adjusting elements.
The disadvantage of the known device is the use of the immersion diodes, which possess uncontrollable axis misalignment of optical scheme and diagrams. The use of immersion diodes results in the complication of the gas analyzer design due to having to add adjusting devices, and in the increase in dimensions.
Known also has been an infrared band gas analyzer (RU 2287803, IPC G01N21/35, publ. Nov. 20, 2006), comprising a wave power source including a light-emitting diode matrix, emitting a reference and operating wave lengths, a gas cell located along the radiation, a main photodetector installed at the cell outlet to receive the reference and operating wave length radiation, as well as a signal processing unit, comprising analog-to-digital coder (ADC), with its outlet connected to a microprocessor and an indication unit. An additional photodetector is installed at the cell inlet, the both photodetectors including pyroelectric photodetectors.
Each light-emitting diode within the light-emitting diode matrix of this known gas analyzer should have fast response when powered by pulse current, to keep the total power unvarying.
When using such matrix, however, it is impossible to facilitate a simultaneous beaming concentration on a single photodetector for each light-emitting diode within the matrix and, at the same time, to minimize optical unit dimensions. Also, the infrared sources are used in the prior art in conjunction with photodetectors of pyroelectric type.
An optical gas sensor, hereinafter referred to as a gas analyzer and known from EP 1995586, IPC G01N21/03, publ. Nov. 26, 2008, comprises a radiation source, an optical gas cell, and an optical radiation detector. Through the optical gas cell, from the inlet to the outlet thereof, two curved channels are formed for passing IR radiation which is emitted from the source located at the inlet of the optical gas cell and is directed towards the detector installed at the outlet of the above-mentioned cell, the channels being spatially separated, their curve radii fitting the body of the optical gas cell. There is a control unit coupled with the radiation source and the optical radiation detector and adapted to change operation modes of the IR radiation source and to process the IR radiation received by the detector displaying the results obtained therefrom.
This gas analyzer possesses such disadvantages as:                substantial losses of the energy of the IR radiation due to having two curved channels for passing same, as well as due to the necessity of the radiation transfer from one channel to another; and        delayed action in operation resulting from slow gas delivery into the channels due to the gas having to self-diffuse inwards the two channels.        
Also known has been a gas monitor comprising IR light-emitting diodes (S. F. Johnston: Gas monitors employing infrared LEDs, Meas. Sci. Technol. 3 (1992) 191-195). A compact version of the monitor provides for registering concentrations of carbon dioxide (CO2). It cannot be used, however, for monitoring methane (CH4) concentrations because, since the absorption factor of CO2 is ten times that of CH4, the monitor for CO2 requires one tenth of optical path length as compared with that for CH4. The impossibility of making a compact version of a hydrocarbon concentration monitor using the design disclosed in Johnston is believed to be a serious drawback of that prior art.
An integrated optical gas sensor known from the GB patent 2401432, IPC G01N21/03, publ. Nov. 10, 2004 and hereinafter referred to as an optical gas analyzer comprises an optical gas cell, an IR radiation source and a detector of this radiation. The optical gas cell is configured to pass IR radiation from its source to the detector of this radiation and is implemented curve-shaped with a rectangular cross-section. A electric bulb is used as a source of IR radiation and is located at the inlet of the cell, and the IR radiation detector is located at the outlet of the cell. There is a control unit coupled with the radiation source and the optical radiation detector and adapted to change operation modes of the IR radiation source and to process the IR radiation received by the detector displaying the results obtained therefrom.
This prior art is selected as the closest analog of the claimed gas analyzer since they have the greatest number of common essential features common with the claimed gas analyzer and are intended to solve similar tasks.
The prior art has such disadvantages as:                substantial infrared radiation energy losses resulting from the curve-shaped implementation of the cell wherein, due to the specificity of the IR radiation reflection from the curved surface of the gas cell internal walls, there is strong dissipation of the radiation energy;        large energy consumption since an electric bulb is used as an IR radiation source, and a pyroelectric detector is used as an IR radiation detector, which results in a control unit to function at low frequencies with lower duty ratio;        a low level of the IR radiation energy registered by the detector due to a large angle of radiation divergence when it leaves the cell and when it reaches the detector, as well as due to the strong IR radiation energy dissipation resulting from the cell curved shape.        
Besides, the optical gas cell developed within this design is not capable to concentrate the IR radiation on the detector plane, since it is implemented as a light guide with reflection from its walls.